[PATCH 04/10] sysfs: Implement __sysfs_get_dentry

[Eric W. Biederman]

This function is similar but much simpler to sysfs_get_dentry
returns a sysfs dentry if one curently exists.

This requires less locking the sysfs_get_dentry and which
makes it preferable in some contexts.

Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
---
 fs/sysfs/dir.c |   38 ++++++++++++++++++++++++++++++++++++++
 1 files changed, 38 insertions(+), 0 deletions(-)

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index cff2b12..3ec9040 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -764,6 +764,44 @@ void sysfs_remove_dir(struct kobject * kobj)
 	__sysfs_remove_dir(sd);
 }
 
+/**
+ *	__sysfs_get_dentry - get dentry for the given sysfs_dirent
+ *	@sb: superblock of the dentry to return
+ *	@sd: sysfs_dirent of interest
+ *
+ *	Get dentry for @sd.  Only return a dentry if one currently
+ *	exists.
+ *
+ *	LOCKING:
+ *	Kernel thread context (may sleep)
+ *
+ *	RETURNS:
+ *	Pointer to found dentry on success, NULL on failure.
+ */
+static struct dentry *__sysfs_get_dentry(struct super_block *sb, struct sysfs_dirent *sd)
+{
+	struct inode *inode;
+	struct dentry *dentry = NULL;
+
+	inode = ilookup5_nowait(sysfs_sb, sd->s_ino, sysfs_ilookup_test, sd);
+	if (inode && !(inode->i_state & I_NEW)) {
+		struct dentry *alias;
+		spin_lock(&dcache_lock);
+		list_for_each_entry(alias, &inode->i_dentry, d_alias) {
+			if (!IS_ROOT(alias) && d_unhashed(alias))
+				continue;
+			if (alias->d_sb != sb)
+				continue;
+			dentry = alias;
+			dget_locked(dentry);
+			break;
+		}
+		spin_unlock(&dcache_lock);
+	}
+	iput(inode);
+	return dentry;
+}
+
 int sysfs_rename_dir(struct kobject * kobj, const char *new_name)
 {
 	struct sysfs_dirent *sd = kobj->sd;
-- 
1.5.3.rc6.17.g1911

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